#define  _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
int main()
{
	int a = 1;
	 
	double sum = 0.0;
	while(a <= 100)
	   
	{    if((a % 2) != 0)
		{
			sum = sum + (1.0 / a);
		     a++;
		}
		else 
		{
			sum = sum - (1.0 / a);
			a++;

		}
		
	}
	printf("%.10lf", sum);

	return 0;
}